The invention relates to novel mechanically stable, powdery pearlescent pigment compositions and their production.
Pearlescent pigments, e.g., bismuth oxy-chloride, mica flakes coated with uncolored or colored metal oxides, natural fish scales and other pearlescent pigments are extremely thin platelets or flakes, which have low mechanical strength and a high tendency to agglomerate. When such pigment flakes are handled in dry form, i.e., as a powder, the platelets are very easily destroyed by rubbing together. The result is reduction of the pearlescence and the luminosity of the pigment.
In order to prevent this reduction in quality, valuable pearlescent pigments are made commercially available in the form of suspensions, because pigments are relatively stable in this form.
However, suspensions have several disadvantages:
(1) the nature of the dispersing agent must be coordinated with the intended use of the pigment by the purchaser;
(2) complicated systems to prevent deposition of the pigment on storage are required, but do not always operate successfully;
(3) the suspension must be packaged so that the liquid dispersing agent neither leaks away nor evaporates.
The foregoing procedures are quite expensive, aside from the fact that large amounts of dispersing agent must, of necessity, be transported, whereby the volume of material transported is unnecessarily increased. Furthermore, liquid dispersing agents are unacceptable for some uses.
Each of these difficulties could be avoided if the pigments could be handled as a dry powder, without reduction of the quality of the pigment. This has not hitherto been possible.
It is known to coat pigments with organic components to simplify the incorporation of pigments, e.g., into synthetic resins. Typical processes for the production of such pigments are described in U.S. Pat. No. 3,650,792, published German Specification Number 2,001,381 and German Patent Specification Number 1,544,830. However, in each of these cases, metal oxide pigments, usually titanium dioxide pigments, which are normally handled as powders, are used. These pigments are mechanically stable owing to a spheroidal shape. Modification of these pigments with organic components merely serves to improve dispersability of the pigments.
Pearlescent pigments have not hitherto been treated in this way. From known results, it could not have been predicted that coating the pigment flakes or platelets, which are very susceptible to breakage, with a solid polymer would provide a pearlescent pigment which can be handled in the form of powder without a noteworthy reduction of quality.
Thus, there has been a continuing need for flaky or platelike pigments which are less sensitive to mechanical stresses than those previously known, but which are not inferior to known pigments in pearlescence or luminosity.
This problem has been solved by the preparation of the pigment compositions according to this invention.
It is an object of the invention to provide powdery pearlescent pigment compositions which are resistant to a loss of properties on handling or shipping as a dry powder.
It is a further object of the invention to provide a process for the production of such powdery pearlescent pigment compositions.
A further object of the invention is the use of the powdery pearlescent pigment compositions in cosmetic formulations.
Other objects will be apparent to those skilled in the art.